1. What every clinician should know

Clinical features and incidence

One of the most common surgical procedures for an obstetrician is primary repair of a perineal laceration, whether spontaneous or after episiotomy. Although anal sphincter injury is not common, with an incidence of 0.6%-6.0%, it is the most severe of the perineal lacerations and thus important to correctly identify.

If not identified your patient may suffer from flatal or fecal incontinence and is at an increased risk of infection. Approximately 85% of women who sustain sphincter injury have persistent sphincteral defects and 10-50% of women with sphincter injuries have anorectal complaints.

The perineal body is made up of the bulbocavernosus muscles, the transverse perineal muscles and the external anal sphincter (EAS) (See Figure 1).

Figure 1.

Muscles of perineal body. Used with permission from Cin-Med, Inc., 127 Main St. N, Woodbury, CT 06798-2915. Copyright Cin-Med, Inc.

Third degree tears involve the external anal sphincter and can be further classified into 3a, 3b and 3c. Fourth degree tears are full-thickness tears through the internal anal sphincter (IAS) and the anal epithelium.

3a: less than 50% thickness of the EAS is torn.

3b: greater than 50% thickness of the EAS is torn.

3c: internal sphincter is also torn.

Risk factors

Nulliparous women have a 7.2-fold increased risk over multiparous women for anal sphincter injury. A midline episiotomy increases the risk for extension of the episiotomy into the anal sphincter. We recommend if an episiotomy is indicated at time of delivery, a mediolateral episiotomy is preferred over midline episiotomy.

Regardless of parity, women who underwent operative vaginal deliveries, whether vacuum or forceps, were at a 3-5-fold increased risk for anal sphincter injury.

Other risk factors for anal sphincter injury are oxytocin administration, epidural anesthesia, advancing gestational age, birth weight greater than 4 kg, occiput posterior position at delivery, shoulder dystocia and vaginal birth after cesarean section (VBAC). It is, however, always possible to sustain a third degree laceration without any of the previously mentioned risk factors.

2. Diagnosis and differential diagnosis

Establishing the diagnosis

Even if you feel your patient has a second degree laceration, a rectal exam can ensure that you are not overlooking a more extensive third or fourth degree tear.

We strongly suggest that every patient who suffers perineal trauma should have a rectal exam to avoid missing isolated tears such as "buttonhole" tears of the rectal mucosa that could possibly be overlooked.

By inserting an index finger into the rectum and the thumb into the vagina you will be better able to feel the tone of the sphincter. Adequate anesthesia is a necessity (epidural is ideal-consider pudendal block if your patient did not have an epidural). An operating room setting with adequate lighting and positioning is recommended to facilitate the repair. Assistants and irrigation are essential.

The biggest pitfalls in the management of an anal sphincter injury are failure to recognize and repair the injury at time of delivery and incorrect repair of sphincter anatomy. If you are at all unsure of the extent of the laceration, consult an experienced obstetrician/gynecologist. We recommend that only a trained clinician repair 3rd and 4th degree lacerations.

3. Management

It is recommended to use a laceration tray including Allis clamps and right angle retractors. In choosing suture material, a delayed absorbable suture should be used to reapproximate the anal sphincter. Standard synthetic sutures show an increased need for removal in the postpartum period over fast-absorbing standard suture.

Studies have shown no difference in the end-to-end or overlapping repair of the anal sphincter. We recommend the use of a broad-spectrum antibiotic at the time of repair such as Unasyn.

3rd degree repair

A rectal exam can improve evaluation of the extent of the injury.

Identify the anatomy. Figure 2 is a cartoon showing the proximity of the internal and external anal sphincter muscles

The internal anal sphincter may be injured; therefore, reapproximation of this area must be the first step. A 3-0 delayed absorbable suture may be used (Vicryl or Monocryl). Place a finger of your nondominant hand in the rectum to elevate the anterior rectal wall (placing the internal anal sphincter on stretch). This aids in placement of the interrupted plicating sutures over the injured area and will improve resting tone of the anus.

The ends of the disrupted external anal sphincter should be identified and minimally mobilized. Dissection extending to 3 and 9 o'clock should be minimized to preserve innervation to the sphincter. Use Allis clamps to grasp the two ends. Approximately four interrupted sutures should be placed (and held with kelly clamps without tying) to bring together the external sphincter. They should be placed at the posterior, inferior, superior and anterior (PISA) aspects of the tubular muscle. This method allows for continued visualization of the sphincter ends until the quadrants of the muscle are identified and incorporated into the repair.

Tie the external anal sphincter sutures in this order: posterior, inferior, superior and anterior so that the sutures will not obstruct each other.

Figure 3.

4th degree repair

Identify the extent of the injury - irrigation and rectal exam facilitates visualization of the injury.

Close the rectal mucosa- If possible knots on the rectal side of the closure is preferable. A running continuous or interrupted closure can be performed with 4-0 delayed absorbable suture (Vicryl or Monocryl).3. Remaining steps of repair are the same as the 3rd degree repair.

4. Complications

Short term outcomes to be expected after repair of an anal sphincter injury are pain, infection and wound breakdown.

Long-term outcomes can include sexual dysfunction (dyspareunia, vulvo-vaginal pain or vaginal stenosis), flatal or fecal incontinence, rectovaginal fistula. Women who experienced a third or fourth degree laceration complained of fecal and flatal incontinence more often than women who did not incur a perineal laceration.

After the repair, the patient should be encouraged to use a peri-bottle or hand-held shower to clean the perineum. Maintain soft to medium consistency of stool with stool softener (Miralax). Always inform your patient about the signs and symptoms of infection

Although infection is rare after a perineal laceration, in the presence of a third or fourth degree laceration infection can be associated with significant morbidity. Also, if your patient had an operative vaginal delivery or if meconium was present there can be an increased risk for infection.

Diagnosis is generally based on the presence of a purulent discharge along with erythema and induration. Treatment includes removing all sutures from the repair. The tear should be irrigated by copious amounts of fluid followed by debridement. The area then needs to be inspected for any necrotic tissue suggesting necrotizing fasciitis. Proper follow-up care should include twice daily dressing changes, sitz baths and broad spectrum antibiotics.

5. Prognosis and outcome

You can inform your patient that 60-80% of women are asymptomatic 12 months after delivery. Those that are symptomatic usually experience flatal incontinence or urgency and if these symptoms arise, to seek care from their physician immediately, as referral to a urogynecologist may be needed for further work-up and treatment.

6. What is the evidence for specific management and treatment recommendations